This invention relates to a lighting device for photography or motion picture photography which is intended to produce an emission of light from a zone which completely surrounds the camera lens.
Such a device is designed to ensure illumination of the subject either without any shadow or with a variable degree of shadow if so required. Moreover, the device is so designed as to make it possible to vary the brightness of reflections from the subject.
There are two methods in use at the present time for the production of shadowless lighting. One of these methods consists in producing light which comes from all directions around the subject in a uniform manner. However, this calls for a very large and costly installation.
Another mode of procedure consists in illuminating the subject in such a manner as to ensure that the shadows cannot be seen by passing the light directly from the axis of the camera lens by means of a semi-transparent and semi-reflecting mirror placed at 45.degree. in front of the latter, a light source being placed on one side at right angles with respect to the axis of the lens. In practice, however, a system of this type is rarely used since its optical adjustment is very difficult and the brightness of reflections is troublesome.
For this reason it has been found preferable to adopt a method of front illumination of the subject by light coming from the zone which surrounds the camera lens. A number of devices designed for this purpose are in any case already in existence but they all have certain disadvantages.
One of these devices consists of a light tube of annular shape which is intended to be placed around the camera lens and may or may not be fitted with an additional reflector. However, if reflectors are employed, they have a low degree of efficiency and, in the case of annular electronic flash tubes, it is found necessary in practice to dispense with the internal reflector on account of the diameter necessary for the camera lens. Morover, the light intensity produced by a device of this type is very limited and the latter does not permit any change in the lighting since there is no possibility of incorporating a means of control due to the shape and small dimensions of a device of this type.
Furthermore, considerable problems are encountered in the case of shiny objects on account of the brightness of reflections. This is due to the fact that the light source has a small surface.
Another device which is employed at the present time for the production of peripheral lighting consists of a fluorescent tube grid having a rectangular shape and intended to be placed around the camera lens, shutters being provided for regulating the quantity of light and changing certain lighting effects.
An apparatus of this type, however, is subject to a certain number of inherent disadvantages. A highly diffused light source cannot be converted to a source of directed light and the power of this apparatus is limited because of the nature of the fluorescent grid. Due to the long length necessary to form the grid, a flash tube cannot be used. Furthermore, an apparatus of this type is not suitable for color photography since the emitted light spectrum is insuitable.
Other devices employed in certain cases comprise a translucent cone of opal material which lights from the outside by one of several independent light sources. The base of the cone is placed against the background provided behind the subject to be illuminated whilst the camera lens is placed in front of an opening formed at the level of the vertex of said cone.
The potential applications of an apparatus of this type are extremely limited, however, and are suitable only for the lighting of close-up still-life pictures. Moreover, part of the light which is projected through the outside of the cone is liable to reach the camera lens and, since the base of the cone is placed against the background, it is impossible to introduce an exposure meter for the purpose of measuring the exposure or to place one's hand in order to rearrange the objects being photographed.